1. Field of the Invention
This invention relates generally to laser engraving, and is concerned in particular with an improved method of laser engraving bent chair crowns and the like.
2. Description of the Prior Art
Laser engraving is now a well known and widely practiced technique. Turnkey laser systems, such as for example the LASER GRAVER marketed by Laser Machining, Inc. of Somerset, Wis., are now in commercial operation. Such systems optically scan a design depicted by black and white art work and simultaneously engrave the design, using a laser beam, into a variety of materials.
Those skilled in the laser engraving art are familiar with the fact that the depth and shape of the laser cut is dependent to a large extent on the position of the focal point of the laser beam relative to the work surface. Thus for example, when drilling holes, if the focal point is located above the work surface, shallow holes of large diameter and with somewhat tapered sides are produced. When the focal point is located at the work surface, deeper holes of uniform diameter are drilled. When the focal point is located below the work surface, shallower holes are again drilled with conical sides.
Because of this phenomenon, laser engraving has been mainly restricted to applications where the work surface is kept at a constant working distance from the laser's focusing lens, which makes it possible to maintain the focal point of the laser beam at the work surface. Thus, cylindrical surfaces such as those of printing cylinders are engraved by being rotated about their axes, whereas flat surfaces on commemorative plaques and the like are shifted to and fro while being incrementally indexed in a single plane. Insofar as we are aware, however, no one has attempted to laser engrave partially cylindrical or curved workpieces, such as for example bent chair crowns.
This is probably because it has been thought necessary to maintain the focal point of the laser beam at the work surface in order to achieve an engraving of acceptable quality. To do so with a partially curved or bent workpiece would require complex manipulating devices and time consuming setup procedures, making the process prohibitively expensive, particularly for limited production lots or customized applications.